Photofabrication, which is now the most widely used technique for precision microprocessing, is a generic term describing the technology used for producing precision components such as semiconductor packages by applying a photosensitive resin composition to the surface of the processing target to form a coating, patterning this coating using photolithography techniques, and then conducting either chemical etching or electrolytic etching using the patterned coating as a mask, and/or electroforming via electroplating.
Recently, reductions in the size of electronic equipment have lead to further developments in higher density packaging of semiconductor packages, including multipin thin film packaging, reductions in package size, and other improvements in packaging density based on two dimensional packaging techniques or three dimensional packaging techniques using flip-chip systems. In these types of high density packaging techniques, connection terminals, including protruding electrodes (mounting terminals) known as bumps which protrude above the package, or metal posts that extend from peripheral terminals on the wafer and connect rewiring with the mounting terminals, must be positioned on the surface of the substrate with very high precision.
The materials used in the above type of photofabrication are typically thick film photoresist compositions. Thick film photoresist compositions are used for forming thick resist layers, and can be used, for example, in the formation of bumps or metal posts by a plating process.
Bumps or metal posts can be formed, for example, by forming a thick resist layer with a film thickness of approximately 20 μm on top of a substrate, exposing the resist layer through a predetermined mask pattern, developing the layer to form a resist pattern in which the portions for forming the bumps or metal posts have been selectively removed (stripped), embedding a conductor such as copper into the stripped portions (the resist-free portions) using plating, and then removing the surrounding residual resist pattern.
Positive photosensitive resin compositions comprising a compound containing a quinone diazide group have been disclosed as suitable thick film photoresists for the formation of bumps or wiring (for example, see patent reference 1).
Furthermore, negative photoresist compositions that can also be used for forming thick films have been disclosed in the patent reference 2 listed below.
(Patent Reference 1)
Japanese Unexamined Patent Application, First Publication No. 2002-258479
(Patent Reference 2)
Japanese Unexamined Patent Application, First Publication No. Hei 8-78318
However, conventional negative thick film photoresist compositions suffer from unsatisfactory alkali developability. In this description, unsatisfactory alkali developability describes the situation where the contrast between the exposed portions and the unexposed portions following alkali developing is unsatisfactory. Deterioration in the alkali developability can cause deterioration in both the resolution and the adhesion of the residual resist pattern following developing, and is consequently undesirable.
Even if a favorable level of alkali developability can be achieved with a resist composition that is typically used for forming thin films for normal semiconductor applications, there is no way of predicting whether a similar favorable result can be achieved if a thick film resist layer is formed using the same composition.